The present invention relates to a system for measuring a substrate thickness and a method thereof; and, more particularly, to an on-line measuring system and a method for accurately measuring a thickness of a substrate during a fabrication process thereof.
Since a lot of defects may develop during a process of fabricating a substrate, various steps for a measurement or an inspection are usually added to the fabrication process to investigate the cause thereof to make correction accordingly, thereby preventing possible development of defects. That is to say, thickness, flatness, transmissivity, bubbles, extraneous substances, and scratches of the substrate are selectively measured or inspected during the fabrication process thereof.
A laser instrument is conventionally adopted for measuring the thickness of the substrate. The laser instrument is an interferometer, which usually includes a laser source, lenses, and detecting sensors. Each of the laser source, the lenses, and the detecting sensors should be precisely arranged with respect to the substrate, and the arrangement thereof is very difficult. Further, the detecting sensors of the laser instrument are conventionally highly sensitive to a mechanical vibration. Therefore, if the substrate moves or vibrates during the measurement, the laser instrument cannot accurately measure the thickness, or even the measurement itself may be impossible.
Accordingly, to use the laser instrument for measuring the substrate thickness, a substrate to be measured is conventionally taken out of a process line before the measurement, and after the measurement a measured substrate is returned into the production line for a next step of the process line. That is to say, though the laser instrument can be used for an off-line measurement, it cannot be used for an on-line measurement.
The off-line measurement, however, requires more manpower and more processing time, thereby causing a high cost as well as a low efficiency. Accordingly, the on-line measurement is preferred to the off-line measurement and various on-line measuring instruments are now developed to make a manufacturing system flexible. Conventional on-line measuring instruments, however, have difficulties in providing an accurate measurement.
It is, therefore, an object of the present invention to provide an on-line measuring system and a method thereof that measure a thickness of a substrate in a production line for fabricating the substrate.
It is another object of the present invention to provide an on-line measuring system and a method thereof where a moving speed and a height variation of a substrate are further measured and the measured values are fed back to be used for an accurate measurement of the substrate thickness.
It is still another object of the present invention to provide an on-line measuring system and a method thereof that provide results of measurements in real time, such that a flexible manufacturing system is made available.
In accordance with one aspect of the invention, there is provided an on-line measuring system for measuring a thickness of a transferred substrate, the system including: a first image detector indicating a vertical variation of a bottom surface of the substrate; a second image detector capturing an image of the bottom surface of the substrate, the bottom surface having two opposite edges; an elevator perpendicularly moving the second image detector with respect to the bottom surface of the glass substrate, the elevator being controlled based on the vertical variation of the bottom surface, such that a vertical distance between the bottom surface and the second image detector remains constant; and a controller for processing the image of the bottom surface to calculate a distance between the two opposite edges of the bottom surface, thereby obtaining a thickness of the substrate.
In accordance with another aspect of the invention, there is provided a method for measuring a thickness of a transferred substrate, the method including the steps of: detecting a transfer speed of the substrate; detecting a vertical variation of a bottom surface of the substrate; capturing an image of the bottom surface of the substrate, wherein a capturing speed and a capturing interval of the image are determined based on the transfer speed while a capturing focus thereof is determined on the basis of the vertical variation, the bottom surface having opposite edges; and processing the image to calculate a distance between the opposite edges of the bottom surface, thereby obtaining a thickness of the substrate.